Refinish primers for repair of damaged coatings of paint are known and used particularly in the automotive industry. After the damaged paint is removed, such primers are ordinarily applied over the exposed bare metal or plastic substrate. They provide intercoat adhesion between the substrate and the decorative/protective top coat and protect the substrate from corrosive substances in the environment. Since heat sensitive parts are usually present, the primers must develop these characteristics without being thermally cured.
Although the traditional refinish primers on the market are adherent to some degree and "cure without heat", they have always poorly resisted solvent attack from organic solvent based overcoats. For today's refinish primers, this has become especially problematic. Refinishers seek formulations having low amounts of solvent so that they can satisfy environmental regulations. In attempting to meet these goals, paint researchers have lowered the molecular weight of the resins present. This change, however, has aggravated the already poor solvent resistance of such formulations. Thus, those refinish primers made for example with air-curable or thermocurable alkyds, epoxy esters, acrylics, melamines, silianes, oil-modified urethanes, nitrocellulose (particularly low molecular weight polymers), two-pack urethanes, and two-pack epoxys often swell, split or distort when overlay coatings are applied.
Microparticles and other materials such as cellulose acetate butyrate have been known since the early 1960's as a means for increasing solids content and for avoiding solvent strike-in in factory applied thermosetting coatings. In these applications, desirable surface characteristics are developed because the thermal treatment melts the microparticles or other weight adding material and smooths the coating surface. Use of microparticles in refinish applications, however, has been avoided for this reason. Refinish paints cannot be heat treated. As a result, a refinish paint formulated with microparticles, microgels or high weight dispersion polymers will have a grainy undesirable appearance owing to lack of thermal smoothing.
Therefore, it is an object of the invention to develop a refinish primer composition with microparticles that can be easily smoothed without heat. Another object is the development of a composition that resists attack of weak and strong organic solvents in the uncured state. A further object is development of a refinish primer and its combination with surfacer that can be worked and handled before they have cured. Other objects include development of a refinish primer composition that minimizes the amount of solvent present and can be effectively smoothed in the uncured state without heat treatment.